Cities seeking more information to improve their services need look no further than the nearest Wi-Fi network.

Smartphone penetration in the developed world is reaching 70%, and most smartphone users have Wi-Fi enabled in order to use their home and work networks. Every Wi-Fi-enabled device continuously pings for available hotspots to connect to, and those pings offer a potential way to track the devices.

Here's how it works: The media access control (MAC) address embedded into any wireless device cannot be changed by the user, and it doesn't change with the cellphone operator. That MAC address is continuously broadcast when the smartphone user has Wi-Fi enabled. As the device interacts with the city's public and private Wi-Fi networks, it provides the user's approximate location, without revealing any personally identifiable information.

Smartphone data could provide cities with information about traffic and people's usage of public transportation in real time. It could populate databases of preferred routes, mixed use of private and public transport, average use of public parking and so on.

Many cities have deployed outdoor Wi-Fi networks as well, for their municipal services, as shown in the Wi-Fi equipment installed on a Barcelona street in the image accompanying this article. These networks are continually used by the police, ambulances, garbage trucks and taxis, plus sensors installed in different areas as part of machine-to-machine deployment. A significant number of cities are also offering free limited Wi-Fi connection for residents and visitors.

Cities need this kind of information. Most municipalities currently use traffic cameras and aggregate information from smartcard usage on public transport to get a glimpse of people's movements, but data is fragmented and limited. Having access to detailed information about how individuals use public transport and private vehicles could help design and optimize public transport, parking and road use.